Time base for use in television systems



July 14, 1942. 1 MAGUlRE 2,289,667

TIME BASE FOR USE IN TELEVISION SYSTEMS Filed March 5, 1941 2 Sheets-Sheet 1 v 4 A 1/ 11131 INVENTOR IRWTN LEONARD MAGUIRE 5V W M "Ms.

July 14, 1942. 1. MAGUIRE TIME BASE FOR USE IN TELEVISION SYSTEMS Filed March 3, 1941 2 Sheets-Sheet 2 ,INVENTOR IRWIN LEONARD MAGUIRE During the time said synchronising signal, no picture elements are.

Patented July 14, 1942 PATENT oFrI I'IME BASE FOR USE IN TELEVISION L SYSTEMS Irwin Leonard Maguire, Elwood, Victoria,

Australia Application March a, 1941, Serial No. 381,510 In Australia March 26,1940

6 Claims. (Cl. 178-4595) The present invention relates to television systems and has primarily been devised to provide a time. base whereby a facsimile of the raster of a transmitter can be synchronously reproduced in receivers. v

In television reception, it is well known that major difficulties arise in the performance of scanning operations which are detrimental to faithful reproduction of a facsimile of the raster at the transmitter and according to known practice it is usual to transmit a synchronising signal .to determine the starting timesfor the lines of the raster. l

occupied in transmission of being recreated thus resultingin a relative loss of brilliancy of the recreated pictures since the recreation of .the pictures does not occur during the whole time that pictures are being viewed,

and further, while said signal controls the starting times i. e. the location at the start for the lines of the raster it does not prevent drift displacement of the required trace of the cathode ray.

Further, the said synchronising signal is impressed upon a carrier frequency which latter is subject to atmospheric andother interferences which tend to mutilate or mar the raster and upset the precise timing of the lines of the raster.

In addition thetransmitting apparatus is unduly complicated by the inclusion therein of means for generating, amplifying and transmitting the said synchronising signal and the apparatus at the receiver is also complicated by the necessary means for separating out and ampli tyin said signal.

According to the present invention the above disadvantages are avoided and the stated objective attained by applying to the control grid circuit of saw tooth oscillators at the transmitter and at .the receiver which oscillators generate beforementioned phased pulses. At the receiver a phase splitter or the like is employed to adjust I and synchronise oscillations thereat with those at the transmitter. Theoscillations first abovementioned may be generated by a condenser in series with a resistance and discharging said condenser by means of a thermionic discharging valve shunted across the latter. Means are provided to apply negative potential across the grid of the discharging valve while the condenser is being charged.

In order to discharge said condenser a positive peaked form of pulse is applied to the grid of said valve. Said positive form of pulse is obtained by utilizing the positive pulses from the E. M. F. above specified which pulses may be used :1 for the starting of peaked forms of pulses, the

discharging valve which is shunted across a charging condenser, the peaked form of positive pulse is applied by a relatively small condenser to the grid of said valve, a relatively large resistance compared to the plate impedance of the saw tooth potentials applied to deflecting electrodes Pf a c'athode ray tube for imparting frame and line sweep movements to cathode rays used for scanning, similarly phased pulses of potential derived from E. M. F. of periodically varying amplitude and having similar characteristics, where- In practising the invention saw tooth oscilla- I tors will be included in the transmitter and receiver the periodicity of the oscillations produced valve connected to said grid being connected 'in series with'a condenser connected to the cathode of said valve. The time constant of the last two mentioned condensers and the resistance connecting the same is preferably relatively small compared with the periodicity time of the said positive pulse so that the peaked pulses of potential applied to these components maybe more sharply peaked. 1

By this preferred arrangement the potential of the charging condenser is raised to a maximum since during the time that the said positive pulse is applied to the grid, the charging condenser is discharged, also grid current flows, thus negatively charging the said relatively small condenser connected to the grid and this charge holds the gridnegative while the charging condenser is being charged thus enabling the potential of the charging condenser to be raised a relatively large amount.

The accompanying schematic diagrams marked thereby being synchronously controlled by the F 8. 1. Fig. 2, Fig. 3 and Fig. depict circuit ar- 1 phase splitter comprises variable condenser Ci,

potentiometer Ri and R2.

Potentiometer Ri and condenser Ci are adjustable to vary the phase angle between the potential across I and 2 and the potential across the resistances of RI and R2.

The potential applied across i and 2 consists of pulses of potential derived from E. M. F. of varying amplitude as before stated.

The variable arm of potentiometer R2 is connected to the grid 2 of the first stage tube Vi so that the signal potential applied thereto may be varied, the plate load of said tube comprising resistor R in parallel with potentiometer R4 shunted thereacross, R4 and R5 being also connected to the tapping point 4 on a potential divider PD comprising resistances R6 to R9 incluive. R4 and R5 are shunted by condenser Ci2.

The plate I of tube VI is connected through coupling condenser G2 with the grid 8 of tube V2 and a resistor R" is also connected to said grid and to point 2 on potential divider PD.

The cathodes of tubes VI and V2 are connected to each other and to point 2 on potential divider PD while an anode load resistor R is connected between plate iii of tube V2 and point 2 on said potential divider.

Points Ii and i2 01 the latter are connected respectively to the postive lead i2 and negative lead i4 of the high-tension D. 0. supply for applying a steady potential to the plates of tubes Vi to V5 inclusive. Inductance Li in the positive lead i2 is connected to point ii and also to condenser CI which latter is connected to said lead between p int ii and inductance Li and to negative lead at i4.

Plate ll of tube V2 is also coupled, via condenser C2 with the grid ii of tube V2, Ri2 being a resistor connected to said grid and to the condenser C4 which latter is also connected to thenegative lead l4.

The plate ll of tube V2 is connected through condenser CI to negative lead i4 and also to output lead It, the latter and lead i2 being the outlet terminals for the sawtooth frame sweep potentials. Potentiometer R4 is connected through Resistor an is connected to grid is of valve 6 V4 and to negative lead i4 and is shunted by condenser Ci4. Condenser C2 is connected from grid it of valve V4 to plate 25 of valve V5.

Resistor RIO is connected to plate 25 of valve V; and to positive lead 2| and resistor Ril is connected from the latter to screen grid 26 of valve VI. Condenser Cl. is connected from said screen grid 22 to negative lead i4. Condenser Cii is connected from plate 22 of valve V4 to control grid 24 of valve VI and tentiometer Ril is connected from said control grid 24 to negative lead. l4.

The valve V4 may be. a pentode, screen grid or triode and valve VI may be a pentode or screen type of valve and the grid 21 may be connected to the grid 24 as shown in Fig. 1 or maybe connected through a condenser or resistance to said grid 24.

Suppressor grid 21 of valve V5 is connected to control grid 24 of valve VI but may be connected izzlirough a condenser or a resistance to said grid In operation with alternating current, potential is applied at points i and 2, the combination of components Ci, Ri and R2 operating to vary the phase of the A. C. potential across RI and R2 with respect to that across i and 2. Potentiometer R2 is used to vary the potential applied to grid 3 of first stage valve Vi Said grid 2 of valve Vi is biased negatively to a relatively large extent so that when the alternating E. M. F. at i and 2 is changing to approximately maximum positive potential, i. e. during a fraction of the time of its periodicity plate current fiows in valve Vi causing equivalent amplified falling plate volts of valve Vi discharging condenser C2. The combined effect of the falling plate volts of valve Vi and the potential or condenser C2 causes an amplified negative peaked transient potential to be applied to the grid 6 of valve V2, the product of capacity of condenser C2 and resistance of resistor Riii being predetermined to give a sharp peak to the said transient potential. Condenser Ci2 affords a bypass for high frequency currents in the plate load R4, R5. The grid 6 of valve V2 is biased to be at zero volts 1. e. so that a suitable direct current plate current flows through said valve. The amplified negative peaked transient potential applied to grid 6 of valve V2 causes the plate cur,- rent of said valve to correspondingly decrease with amplified eflect, thus causing its plate voltage to rise producing a corresponding positive transient peak. The plate potential of valve V2 may be considered as made up of a direct current potential component and an approximately square topped form of fluctuating potential. The capacity of condensers C2 and C4 and of the resistance Ri2 are predetermined so that the approximately square topped wave of plate potential of valveV2 and the corresponding potential of the latter and A the corresponding potential drop across resistance Rii results in a wave of alternately positive and negative sharply peaked transient potentials between grid i5 of valve V2 and negative lead i4.

The resistance Ri2 is arranged to be relatively large compared to the plate resistance of valve V2 and size andcapacity of condenser C4 is not critical but is preferably larger than condenser C2. When positive potential is impressed on grid ii of valve V2 condenser C5 discharges through said valve and grid current also flows, thus the plates of condenser C2 which are connected to saidgrid are charged negatively.

Further condenser C4 is charged to a small potential depending upon the size of its capacity and the resistance of Ri2. Negative potential of C3 on grid i5 of valve V2 prevents plate current flowing through the latter while condenser C5 is being charged. when the negative peaked transient potential pulse is applied across C2, Ri2 and C4 the negative charge of condenser C2 is reduced by the discharge of condenser C4 and by leakage of the respective charges of said condensers i. e. the negative potential applied to grid ii of valve V2 is slightly reduced to an amount which is less than the potential of the charge given to it when the next positive transient pulse is applied across C3, RII and 04, but the potential of said negative charge is still great enoughto prevent plate current flowing through valve V3. when the next transient positive pulseoi potential is applied across C3, RI2'and'Cl the condenser .05 is discharged, grid current iiows and the negative charge of condenser 03 is again increased toan amount corresponding to the positive potential of the transient pulse; Thus the grid It of valve V3 is held at a relatively high negative potential which is slightly less than the applied potential of the positive peaked transient pulses enabling the condenser C to be discharged on 'the application of the said last mentioned off at charging and discharging of condenser US.

In Fig. 1 the potential across condenser C5 is applied to the terminals I8 and I 8 for the frame sweel potentials.

The direct current potential applied to negative lead It and positive lead I3, to supply power for the operation of the valves VI, V2 and-V3, is relatively high compared to the potentials required across C3,.RI2 and Cl and the potentials for said power supply to valves VI and V2 are obtained by the use of the potential divider PD the potential for valve VI being obtained from tapping point 4 and the potential for V2 from point 9 of PD. The cathode bias for valves VI and V2 is obtained from point; 8 of PD enabling the use of the latter, with its separate connections for power supply to valves VI and V2,-to reduce unwanted oscillations, and, also the application" of the relatively considerable negative potential bias to be applied to beforementioned. Y

The filter consisting of inductance LI and condenser Cl provides for a smoother direct current potential to be applied acrom RI3 and valve V3 and also to PD at points II and I2.

The multi-vibrator consisting of the valves V4 the grids of valve VI as ter, is used for production of the line sweep potentials which may conveniently be taken acrosscondenser CI I. Potentiometer RI'I may conveniently be used to vary the frequency of the line sweep potentials.

In the modified circuit arrangement in Fig. 2 amplifying valves V6 and V! are located between the output leads It and I8 and valve V3. In addition, condenser Cia is connected in series with condenser 05 and to negative lead It. Condenser CSI) is connected between condensers C5 and C511 to grid 25 of valve V6 and grid leak re-- sistance RI! is connected to said grid and to negative lead II.

Plate 26 of valve V6 is connected to resistance R2I connected in series with potentiometer R2! to positive lead I3. Condenser OH is connected to movable arm of potentiometer R20 and the grid 21 of valve VI. Grid leak resistance R22 is connected to said grid 21 and to negative lead ll. Resistance R24 is connected to plate 23 of valve V1 and to positive lead I3. v Cathodes 2! and of valveVi and V1 respec tively are connected together and resistance R23 and vs and components associated with the latdescribed in Fig. 1.

This modified arrangement operates to sim- 7 leads Ito and Ila are respectively connected to plates 21 and 28 of valves Vl and-V6 respectively.

Output leads ltd and Ilc correspond to output terminals liand I3inFig.l.

The valves V4 and V5 in Fig. 2 with their associated components constitute'the oscillatorfor the line sweep potentials. It will benoted 7 that valve V4 is shown as a pentode thus having 1 a higherv plate impedance than the triode valve .Vlin Fig. l which is more suitable for giving higher frequencies to said potentials.

It wilibe noted that the amplifying valves V6 and V1 with associated components are connected together in paraphase. the connections of condenser C5 and 05a being arranged to act as a potential divider so as to reduce. the amount of potential applied to grid 26 of valve V6.

The inclusion of the amplifying valves V6 and V1 provides a greater potential difference for a given potential drop across I3 and I4 and is arranged so that the output voltage at ,Iia and Ian shall be symmetrical about the earth potential of the cathode ray tube.

The potential applied to the grid 21 of valve VI viathe potentiometer-R20 is preferably -arranged to be equal to that-applied to the grid 25 of valve V6. The time constant of resistance RI! and condenser C5!) is preferably arranged to be approximately equal to the time constant of condensers 05a, C5 in series with resistance RI3. By this preferred arrangement the preferred'saw tooth form of potential is obtained across the output terminals of the leads I61; and Ida.

Referring now to Fig. 3 in the modified circuit arrangement shown therein valves VI and V2 (shown in Figs. 1 and 2) and the components associated therewithare omitted and a potential from an alternating E. M. F. is applied to points lo and 20 which correspond to I and 2 in Figs. 1 and'2. In Fig. 4 the suffixes lb. 2b, 3b etc. correspond to suffixes I, 2 and 3 etc. of Fig. 1 and components CIb, Rlb, R22: etc. correspond to components CLRI, R2 etc. in said Fig. 1

In this modified arrangement sharply peaked potentials are not applied across condenser 03b, RI2b, Clb but alternating potentials are applied which correspond to the alternating potentials applied to lo and 2c. The output potentials of condenser Cib is arranged as. before plify circuit arrangements but as before stated the arrangement as in Fig. 1 whereby sharply peaked transient potentials are applied across grid Ii of valve V3 and negative lead ll, all things being equal is preferred, because for a given potential applied to positive lead I3 and negative lead It sharper changes in output potential and a relatively greater change of potential is obtained thereby.

Referring now to Fig. 3 the suflixes Ic, 2c, 30 etc. correspond to suflixes I, 2, 3 etc. of Fig. 1, the modified arrangement in Fig. 3 is similar to that in Fig. 4 except that a diodevalve V8 in series with potentiometer R26 is shunted across the movable arm of potentiometer R2'c and negative lead Ilc which latter correspond to It and Ilb in Figs, 1 and 2 and 3 respectively. Condenser C3c, RI2c and C40 areshunted acrossan approximately square topped wave form of 3 is connected to said cathodes and to negative lead I I ll and is shunted by. condenser CI2. Output potential across the potentiometer R26 which as above indicated is preferred to the arrangement shown in Fig. 3 in which latter a sinusoidal form of alternating potential may be applied across potentiometer R2b.

It will be readily appreciated that the frequency of the saw tooth sweep potentials, at output terminals at l6, I! in Fig. I and the corresponding terminals in Figs. 2', 3 and 4 is the same as the frequency of the alternating potential pulses applied across terminals l and 2 in Fig. 1 and the terminals corresponding thereto in Figs. 2, 3 and. 4.

I claim:

1. In television systems and for the purpose specified, generating means for creating saw tooth oscillations at the receiver and at the transmitter, means for adjusting the phase of said oscillations at the receiver, a source of E. M. F. of periodically varying amplitude and having similar characteristics at both the transmitter and receiver, means for applying pulses of potential derived from said E. M. F. to the control grid circuit of said generating means, means for applying the output of said generating means to the deflecting electrodes of a cathode ray tube for scanning at both the transmitter and receiver, said generating .means comprising a condenser in series with a resistance, a thermionic valve shunted across said condenser and operating to charge the latter when a positive peaked form of aforesaid pulses is applied to the control grid of said valve, and means to apply negative potential tosaid grid while said condenser is being charged.

for generating a substantially square topped wave of potential from a substantially sinusoidal wave potential, an electron discharge device having cathode, grid and anode, a resistance and capacity series circuit in which the resistance is large compared to the plate resistance of said electron discharge device,

, connected for applying waves of alternately positive and negative sharply peaked transient potentials derived from said first means between the grid and cathode of said electron discharge device for producinga saw tooth wave potential in the output of said electron discharge device.

4. Apparatus as set forth in the preceding claim 3 further comprising amplifying means having an input circuit, and coupling means consisting of a resistance and capacity circuit in the input of said amplifying means and a resistance capacity circuit in the output of said electron discharge device, said resistance capacity circuits having substantially the same time constants.

5. Apparatus as set forth in claim 3 in which the means for generating a substantially square topped wave potential from a substantially sinusoidal wave potential consists of a rectifier connected in series with a potentiometer and across a source of substantially sinusoidal wave potential supply.

6. In a television system, an oscillator for generating saw tooth potentials applied to the deflecting electrodes of a cathode ray tube for imparting frame and sweep movements to the cathode rays used for scanning, comprising: means for generating a substantially sinusoidal wave potential, an electron discharge device having cathode, grid and anode, a resistance and capacity series circuit in which the resistance is large compared to the plate resistance of said electron discharge device, connected for applying waves of alternately positive and negative sharply peaked transient potentials derived from said first means, between the grid and cathode of said electron discharge device for producing a saw tooth wave potential in the output of said electron discharge device.

' I. L. MAGUIRE. 

